5.1.4 - hormonal communication

• in protein hormones, the first messenger is a hormone. the hormone binds to receptor on the cell surface membrane as they are complementary. this activates the enzyme adenylyl cyclase. the enzyme activates the second messenger cyclic AMP. cAMP triggers a response inside the cell
• endocrine communication is when a hormone is released by an endocrine gland into the blood. endocrine communication is ductless.
• endocrine glands contain cells that produce a hormone and release it straight into the blood
• exocrine glands produce a hormone which is not directly released into the blood.
• There are two types of hormones:

  peptide hormones

  steroid hormones
• peptide hormones must use the first messenger second messenger model as they are not soluble in the membrane
• steroid hormones act upon the DNA in the nucleus as they can pass through the cell membrane
• Hormone is the first messenger
• endocrine communication is when specialised glands secrete hormones into the bloodstream.

  the circulatory system carries hormone to target cell.
• Adrenal glands are located above the kidneys. Adrenal cortex is the outside layer with the adrenal medulla in the middle.
• Adrenal medulla secretes adrenaline in response to danger or stress as part of the fight or flight response.
• The adrenal cortex secretes aldosterone which targets salt concentration.

  It also secretes cortisol which increases blood glucose concentration.
• Pancreas has pancreatic islet which has alpha cells, beta cells and the exocrine acinus.
• it is important that blood glucose concentration remains stable to maintain a constant blood water potential to prevent osmotic reaction of cells.

  also important to maintain a constant concentration of respiratory substrate
• Glycogenesis is when the liver converts glucose into the storage polymer glycogen.
• Glycogenolysis is when the liver hydrolyses glycogen into glucose which can diffuse into the blood.
• Gluconeogenesis is when the liver converts glycerol and amino acids into glucose
• When blood glucose concentration decreases:

  1. alpha cells in islets of langerhans in pancreas detect decrease and secrete glucagon into blood
  2. glucagon binds to cell surface receptors on liver cells (hepatocytes) and activates enzymes for glycogenolysis and gluconeogenesis
  3. glucose diffuses from liver into blood stream
  4. alpha cells detect that blood glucose concentration has returned to optimum and stop producing glucagon.
• Glucagon works by:

  hormone receptor complex forms

  conformational change to receptor activates G protein.

  Activates adenyl cyclase which converts ATP to cyclic AMP

  cAMP activates protein kinase A pathway

  results in glycogenolysis
• When blood glucose concentration increases:

  1. Beta cells in islets of langerhans in pancreas detect increase and secrete insulin into blood
  2. insulin binds to cell surface receptors on target cells to:
  3. increase cellular glucose uptake
  4. activate enzymes for glycogenesis (liver and muscles)
  5. stimulate adipose tissue to synthesise fat
• Insulin leads to a decrease in blood glucose concentration by:

  increases permeability of cells to glucose

  increases glucose concentration gradient

  triggers inhibition of enzymes for glycogenolysis
• Insulin secretion is controlled because:

  beta cells have potassium and calcium ion channels to maintain potential difference of -70 mV

  as glucose concentration increases, glucose enters beta cells

  respiration of glucose produces ATP. ATP gated potassium ion channels close so potassium ions no longer diffuse out of cell.

  Potential difference in cell becomes more positive which leads to depolarisation.

  calcium ion channels open which triggers exocytosis of insulin.
• The exocrine function of the pancreas is that is secretes digestive enzymes to the duodenum via the pancreatic tract.
• Type 1 diabetes mellitus is caused when the body cannot produce insulin due to an autoimmune response which attacks beta cells.
• type 1 diabetes mellitus is treated by insulin injections from a source of genetically modified bacteria. as well as regular blood glucose concentration checks.
• Type 2 diabetes mellitus is caused when the glycoprotein receptors are damaged or become less responsive to insulin

  strong positive correlation with poor diet and obesity
• type 2 diabetes mellitus is treated by controlling diet and having good exercise as well as checking blood glucose concentration.